Question

A company specification calls for a steel component to have a minimum tensile strength of 1240 MPa. Tension tests are conducted on selected samples, but all components are also subjected to Vickers hardness testing. (A) What HV (in Kgf/mm2 ) is the minimum acceptable value? (B) If hardness is measured using Rockwell C hardness test, what is the minimum HRC value that is acceptable?

Answer 1

Answer:

a) The minimum acceptable value is 387.5 HV using Vickers hardness test.

b) The minimum acceptable value is 39.4 HRC using Rockwell C hardness test.

Explanation:

To get the tensile strength of a material from its hardness, we multiply it by an empirical constant that depends on things like yield strength, work-hardening, Poisson's ratio and geometrical factors. The incidence of cold-work varies this relationship.

According to DIN 50150 (a conversion table for hardness), the constant for Vickers hardness is ≈ 3.2 (an empirical approximate):

$\mbox{Tensile strength}=HV*3.2\\\\HV = \frac{\mbox{Tensile strength}}{3.2} =\frac{1240}{3.2}=387.5$

According to DIN 50150, the constant for Rockwell C hardness test is ≈31.5 around this values of tensile strength:

$\mbox{Tensile strength}=HRC*31.5\\\\HRC = \frac{\mbox{Tensile strength}}{31.5} =\frac{1240}{31.5}=39.4$